It is the intent of all sustained-release pharmaceutical preparations to provide a longer period of pharmacologic effect after the administration of a drug than is ordinarily experienced after the administration of immediate release preparations of the same drug. Such longer periods of efficacy can provide many inherent therapeutic benefits that are not achieved with corresponding immediate release preparations. The benefits of prolonged analgesia afforded by sustained release oral analgesic preparations have become universally recognized and oral opioid analgesic sustained-release preparations are commercially available.
Prolonged analgesia is particularly desirable in patients suffering from moderate to severe pain, such as cancer patients. Available oral preparations provide a duration of effect lasting e.g., about twelve hours (and sometimes 24 hours) such that a drug may only have to be administered to a patient one to three times a day. For example, morphine, which has been considered to be the prototypic opioid analgesic, has been formulated into twice-daily, oral controlled release formulations (e.g., MS Contin.RTM. tablets, commercially available from The Purdue Frederick Company).
Another approach to sustained delivery of a therapeutically active agent are transdermal delivery systems, such as transdermal patches. Generally, transdermal patches contain a therapeutically active agent (e.g., an opioid analgesic), a reservoir or matrix containing the opioid or other active ingredient(s) and an adhesive which allows the transdermal device to adhere to the skin, allowing for the passage of the active agent from the device through the skin of the patient. Once the active agent has penetrated the skin layer, the drug is absorbed into the blood stream where it can exert a desired pharmacotherapeutic effect, such as analgesia.
Transdermal delivery systems in which an opioid analgesic is the active ingredient have been contemplated. For example, a commercially available opioid analgesic transdermal formulation is Duragesic.RTM. (commercially available from Janssen Pharmaceutical; active ingredient is fentanyl). The Duragesic.RTM. patch is said to provide adequate analgesia for up to 48 to 72 hours (2 to 3 days).
Buprenorphine, a partially synthetic opiate, has also been contemplated for prolonged analgesia. Although other types of opioid analgesic transdermal formulations have been reported in the literature (such as fentanyl, discussed above), buprenorphine transdermal delivery systems are of particular interest because buprenorphine is a potent, partial agonist opioid analgesic with desirable therapeutic properties. For example, buprenorphine is 50 to 100 times more potent than morphine, but has a much safer therapeutic index than morphine (see Wallenstein S L, et al., Crossover Trials in Clinical Analgesic Assays: Studies of Buprenorphine and Morphine, Pharmacotherapy, G(5): 225-235, 1986 hereby incorporated by reference). Further, the partial agonist properties of buprenorphine are useful in the treatment of opioid addiction.
There are several types of transdermal formulations of buprenorphine reported in the literature. See, for example, U.S. Pat. No. 5,240,711 (Hille et al.), U.S. Pat. No. 5,225,199 (Hidaka et al.), U.S. Pat. No. 5,069,909 (Sharma et al.), U.S. Pat. No. 4,806,341 (Chien et al.), and U.S. Pat. No. 5,026,556 (Drust et al.), all of which are hereby incorporated by reference.
Buprenorphine has a low oral bioavailability and has been considered by certain of those skilled in the art to be like other narcotics which are habit-forming (see, e.g., U.S. Pat. No. 5,240,711 to Hille, et. al.) and induce tolerance (see, e.g., U.S. Pat. No. 5,613,958 to Kochinke, et. al.). As reported in Hille, et.al., experts are of the opinion that the form of administration of a medicinal drug contributes to the risk of addiction, and higher than necessary blood levels created immediately after administration of a drug such as buprenorphine, followed by a drastic decrease (causing in succession euphoria and then ineffective pain treatment), cause the patient to start to long for the next dosage (referred to as an "iatrogenic" addiction). In the case of buprenorphine, Hille, et al. reported that continuous infusion would be considered the most suitable mode to avoid such an iatrogenic addition by providing constant blood levels; however, continuous infusion requires physician control and insertion of a cannula (which may cause inflammation at the site). This problem is considered to be overcome by Hille, et al. by virtue of their use of a transdermal delivery system which includes buprenorphine or one of its pharmaceutically compatible salts and which releases the drug over a period of at least 24 hours in a controlled manner, and ensures that the buprenorphine does not notably decompose when the transdermal delivery system is stored, and which further ensures that the buprenorphine in-vivo penetrates through the skin at the required amount.
Kochinke et al. describe a transdermal system for the modulated administration of tolerance-inducing drugs. Buprenorphine is identified therein as such a drug. The system is designed to deliver the drug through the patient's skin via a three-phase drug delivery profile. In the first phase, which begins with patch application and ends at 2-10 hours after patch application, plasma levels of the drug are obtained. This phase is followed by a second phase in which therapeutic plasma levels of the drug are maintained. The second phase begins at about two to ten hours after patch application and ends at about 8-18 hours after patch application. In a third phase, sub-therapeutic levels of the drug are maintained, via inherent patch design and/or patch removal. The rationale behind the drug delivery profile of Kochinke et al. is that initial high blood levels may be more effective when followed by a period of decreasing dosage (down to sub-therapeutic levels), than if the blood levels are maintained either at the higher or lower level (i.e., sub-therapeutic levels) throughout the entire administration period. By virtue of this modulated profile, it is said that the onset of tolerance to the drug being administered can be prevented or greatly reduced.
Despite these advances in the art, there remains a need for methods of treating patients with buprenorphine that provide effective analgesic levels of buprenorphine for prolonged periods of time while eliminating or minimizing dependence, tolerance, and side effects, thus providing a safe and effective method of pain management.